The present invention relates to a device for making a drilled hole with an undercut, particularly in a facing panel made of ceramics, stone, concrete or the like.
A known device for making a drilled hole with an undercut consists of a drilling machine for producing a torque, a drilling tool for engaging a facing panel to form a drilled hole therein; holding means of a supporting stand having a swivel bearing for receiving and mounting the drilling machine so that it can swivel with the drilling tool attached to it and an adapter receiving the drilling tool, which is connectable to the drilling tool and the drilling machine so as to transfer torque from the drilling machine to the drilling tool.
To produce a drilled hole with an undercut, devices are known which have a bearing bush with a concave recess in which a drilling tool provided with a convex collar is supported and mounted so as to swivel. By swivelling out the drilling tool while simultaneously performing a stirring movement, lateral cutting edges provided on the drilling tool ream out an undercut in the region of the bottom of the drilled hole. An expansible fixing plug with an expansible sleeve can be inserted and fixed in the undercut in an interlocking manner.
Such drilled holes with an undercut can also be made in a facing panel or similar structure, but in that case the undercut must be made very exactly, so that, when an expansible anchor is inserted and expanded, the expansion pressure that is produced is not too great. To produce an exact undercut, these devices are designed to allow an automatic, machine-controlled swivelling. In addition, drilling tools that have a drilling head set with diamond chips are used. When the drilling tool clamped in alignment with the drive axis of the drilling machine digs into the facing panel, the entire end face of the truncated cone-shaped drilling head comes into engagement. This requires a high contact pressure of the drilling tool, which leads to the diamond chips becoming prematurely blunt, because of the slower cutting speed in the center of the end face of the drilling tool. This considerably reduces the service life of the drilling tool.